In general, an excavator, in particular, an electric excavator is constructed such that its upper swing structure includes a part of a turning point, and thus hydraulic source from the upper swing structure can be transferred to a lower traveling structure without using a hydraulic wiring. For this reason, even in the middle of the swing operation of the upper swing structure of the equipment, the hydraulic source form the upper swing structure can be supplied to a hydraulic motor for traveling of the lower traveling structure to enable the traveling operation to be performed. However, in the electric excavator (or hybrid excavator), in the case where an electric motor is used instead of the hydraulic motor, a power transfer device is needed which has the same concept as that of an existing hydraulic turning joint.